diff --unified -u -r urlgrabber-3.9.1.orig/urlgrabber/mirror.py urlgrabber-3.9.1/urlgrabber/mirror.py
--- urlgrabber-3.9.1.orig/urlgrabber/mirror.py	2014-09-16 14:44:54.582048746 +0200
+++ urlgrabber-3.9.1/urlgrabber/mirror.py	2014-09-16 14:49:24.138034099 +0200
@@ -88,6 +88,7 @@
 
 
 import random
+import urlparse
 import thread  # needed for locking to make this threadsafe
 
 from grabber import URLGrabError, CallbackObject, DEBUG
@@ -366,11 +367,12 @@
     # by overriding the configuration methods :)
 
     def _join_url(self, base_url, rel_url):
-        if base_url.endswith('/') or rel_url.startswith('/'):
-            return base_url + rel_url
+        (scheme, netloc, path, query, fragid) = urlparse.urlsplit(base_url)
+        if path.endswith('/') or rel_url.startswith('/'):
+            return urlparse.urlunsplit((scheme, netloc, path + rel_url, query, fragid))
         else:
-            return base_url + '/' + rel_url
-        
+            return urlparse.urlunsplit((scheme, netloc, path + '/' + rel_url, query, fragid))
+
     def _mirror_try(self, func, url, kw):
         gr = GrabRequest()
         gr.func = func